1. Field of the Invention
This invention relates in general to downhole electrical submersible pump (“ESP”) electronics and, in particular, to downhole ESP assemblies which utilize active semiconductor circuitry to disconnect or regulate voltage to downhole electronics for protection in the event of a power surge or grounded phase.
2. Description of the Prior Art
In conventional submersible pump installations, there may be a system for monitoring various characteristics of the pump motor environment, such as pressure, vibration, and temperature. Due to the extreme conditions inside a well, it is important to be continuously aware of these downhole operating characteristics. The temperature is often 200° F. or higher, while the voltage and current being supplied is also at high levels.
There are various methods used to monitor downhole operating characteristics. A surface unit typically monitors these and other conditions via data sent from a downhole unit. For example, the temperature of the motor provides an indication of the pump's operating efficiency. As such, a temperature probe located within the motor can provide an indication of whether or not the motor is overheating, which may possibly lead to motor failure.
Submersible pump installations include a large horsepower electric motor located in the well. The electric motor receives three-phase AC power via a power cable extending from the surface with voltages phase-to-phase being commonly 480 volts or more. The electric motor drives a pump, of varying types, to pump well fluid to the surface. The downhole gauge is used to monitor the downhole characteristics. The gauge is in a housing connected to the bottom of the motor. The gauge is coupled to the neutral node or Y point of the three-phase power windings of the motor via an inductor of very large inductance. The large inductor is used to filter out the motor AC in order to prevent the AC from interfering with communication signals transmitted between the downhole unit and surface unit. The large inductors also work to protect the gauge from voltage surges caused by varying phenomena, such as when one phase of the three phase power becomes grounded, which results in a high voltage at the three phase “Y” point of the motor.
This prior art approach has numerous disadvantages. For example, the inductors are large and very expensive. Also, the high inductance and capacitance values of the protection circuitry restrict the communications bandwidth through the protection circuitry. In addition, the inductors create a large leakage current to ground as the output is typically limited with a zener diode, which can cause corrosion in cases of higher voltages.